Showing papers by "Oklahoma State University–Stillwater published in 1983"

Optical transitions of Er 3 + ions in fluorozirconate glass

Abstract: Optical-absorption, -emission, and -excitation spectra are presented for ${\mathrm{Er}}^{3+}$ ions in fluorozirconate glass. Measured oscillator strengths of the transitions between $J$ manifolds at 300 and 15 K are compared with calculated electric and magnetic dipole oscillator strengths. Radiative rates for five luminescing states were calculated. The nonradiative rates from these excited states were determined by calculating the difference between the measured rates and the calculated radiative rates. The low-temperature nonradiative rates are in agreement with the phenomenological energy-gap law followed by rare-earth ions in a number of crystals and glasses. The temperature dependence of the lifetimes was analyzed using the Huang-Rhys theory of multiphonon emission. Values for the $^{4}I_{\frac{11}{2}}$ radiative and nonradiative rates obtained by the above methods are compared with those obtained applying the method Flaherty and DiBartolo used to study Mn${\mathrm{F}}_{2}$: ${\mathrm{Er}}^{3+}$. The multiphonon emission rates in fluorozirconate glass are much lower than the rates for the same levels of ${\mathrm{Er}}^{3+}$ in oxide glasses. Measurements of the bandwidths of the ground and excited states of ${\mathrm{Er}}^{3+}$ and the nearly exponential decay of the emissions indicate a relatively narrow distribution of site symmetries compared to oxide glasses.

Further characterization of the E 1 ′ center in crystalline Si O 2

Abstract: Electron-spin resonance (ESR) is used to investigate the formation and thermal anneal characteristics of ${E}_{1}^{\ensuremath{'}}$ centers in high-quality synthetic quartz. These centers are produced by ionizing radiation near room temperature followed by annealing to 300\ifmmode^\circ\else\textdegree\fi{}C. The resulting concentration depends on the specific irradiation temperature, the nature of previous irradiation and thermal anneals, and whether the sample is air swept or unswept. Migration of interstitial alkali ions (${\mathrm{Li}}^{+}$ and/or ${\mathrm{Na}}^{+}$) as a result of irradiation correlates with the production of the ${E}_{1}^{\ensuremath{'}}$ centers, and a relationship between the ${[\mathrm{A}\mathrm{l}{\mathrm{O}}_{4}]}^{0}$-center concentration and the ${E}_{1}^{\ensuremath{'}}$-center concentration is also observed. Electron-nuclear double resonance is used to show that the two "weak" hyperfine interactions (8- and 9-G splittings) are with $^{29}\mathrm{Si}$ nuclei. From the angular dependence of the ESR data taken at 300 K, complete sets of spin-Hamiltonian parameters are determined for the $\stackrel{\ensuremath{\leftrightarrow}}{g}$ matrix and the three $^{29}\mathrm{Si}$ hyperfine (one strong and two weak) matrices.

Isolation of motile spermatozoa by density gradient centrifugation in Percoll

Abstract: A procedure using centrifugation in density gradients composed of Percoll was developed for isolation of spermatozoa from mammalian semen. To evaluate the technique, rabbit, human, or bovine semen was layered over continuous Percoll gradients ranging in density from 1.02 to 1.13 gm/ml and centrifuged at 1,500g for 45 min. After centrifugation, the seminal plasma remained above the gradient, whereas the spermatozoa and seminal particles were distributed within the gradient according to their buoyant densities. Unlike most washing techniques, no sperm pellet was formed; instead, the spermatozoa were concentrated into a compact band above the most dense layer of Percoll. The spermatozoa recovered from the gradient were easily resuspended by gentle techniques. Thus, the mechanical stress to the spermatozoa was minimized. Osmotic stress to the spermatozoa was also negligible as the Percoll gradients were isotonic throughout. Spermatozoa obtained by this technique possessed motility equivalent to that of spermatozoa in the unfractionated semen. Sperm suspensions recovered from the gradients contained less than 5% of the nonspermatozoal particles present in the original samples of unfractionated semen. Soluble seminal components were also efficiently removed from the spermatozoa. Thirty billion bovine spermatozoa could be fractionated on a single gradient without loss of effectiveness. Recovery of spermatozoa from these preparative separations averaged 80%. These results demonstrated that Percoll was a superior medium for efficient density gradient isolation of motile spermatozoa free of contamination by other seminal constituents.

Nitrogen metabolism of ruminant animals: historical perspective, current understanding and future implications.

Abstract: Nitrogen metabolism of ruminant animals has been the subject of thousands of research publications. Study of ruminal and intestinal function continues. The quantitative and qualitative importance of ruminal microbes as a source of protein have become apparent in many trials, and factors controlling microbial protein synthesis or growth of microbes as well as ruminal degradation of dietary protein have been explored. Information on the supply side of the protein ledger (ruminal synthesis, bypass or escape of dietary protein; intestinal digestion) exceeds current knowledge of quantitative needs for amino acids. Descriptive models of N metabolism have evolved that amalgamate current concepts. With future amendments, these systems should prove useful in diet formulation to more fully utilize ruminal fermentation and increase productive efficiency of ruminant animals. Expanding knowledge of ruminal N metabolism will permit greater control and manipulation of the processes of ruminal fermentation and postruminal digestion.

Landownership and the Adoption of Minimum Tillage

Abstract: Full-owner operators and landowners with small holdings have lower minimum tillage adoption rates on cultivated cropland than do other landownership groups after accounting for land quality and regional location. Nonfamily corporate structure does not significantly influence the adoption decision. These conclusions about minimum tillage adoption were obtained from a logit model using 7,649 cultivated cropland observations from across the United States. This study indicates that small operating size poses more of an obstacle to minimum tillage adoption than does separation of ownership from farm operation.

Sheared colloidal suspensions

Abstract: The structure of aqueous suspensions of electrostatically interacting submicron polymer spheres is studied as a function of shear. These model colloidal suspensions exhibit a variety of equilibrium and nonequilibrium structures and phase transitions. Both shear induced melting of solid-like structures and shear induced distortion of liquid-like structures are observed. Several models are presented to explain the observed effects. The analogy between these colloidal suspensions and pure fluid systems is discussed.

Microhabitat preferences of benthic fauna in a woodland stream

Abstract: Estimates of numbers, biomass, and diversity of benthic macroinvertebrates were made quarterly over a two-year period to investigate microhabitat preferences. Although biomass of most taxa was significantly different among sampling times, physical factors also appeared to be important in determining abundance of many taxa. Optimum depth, velocity, substrate type, and turbulence were determined for major taxa. Optimum conditions for diversity appeared to be 34 cm depth, 60 cm s−1 velocity, and rubble and boulder substrate type. Habitat preference functions were derived for several taxa based on significant polynomial regressions of biomass on depth, velocity, substrate, and Froude number (turbulence). The relationship between abundance and physical habitat conditions was tested by using the product of the preference factors (range: 0–1) for depth, velocity and substrate type as a measure of habitat suitability (joint preference factor). There were significant correlations between biomass [transformed by loge (x + 1)] of 10 benthic species and the joint preference factor. The joint preference factors accounted for from 11 to 61% of the variation of biomass of the 10 benthic species. The intercepts of the relationships between biomass of individual species and the joint preference factor were not significantly different from zero for any species. Therefore, the joint preference factors appear to be valid indicators of biomass. The preference functions have utility in habitat assessment studies, specifically with regard to minimum instream flow determinations.

Agricultural and food policy

Abstract: Part I Process The Policy Setting Policy Problems of Food and Agriculture The Policy Process Food and Agricultural Policy Interest Groups. Part II International Trade and Macroeconomic Policy The World Food Problems The Role of Trade International Trade and Market Development Policy The Macroeconomics of Agriculture. Part III Domestic Farm and Resource Policy The Farm Problem Domestic Farm Policy Resource Policy The Structure of Agriculture. Part IV Consumers, Rural Development and Agribusiness Food Price Policy Nutrition, Food Safety, and Food Quality Rural Development Policy Impact of Agricultural and Food Policy on Agribusiness National Agricultural and Food Policy.

Luminescence from oxygen vacancies in MgO crystals thermochemically reduced at high temperatures

Abstract: Experimental measurements and theoretical calculations are reported which may resolve some of the remaining difficulties associated with photoemission from anion vacancies in thermochemically reduced MgO crystals. The intensities of the 2.3- and 3.2-eV luminescence bands are found to be strongly influenced by both the concentrations of ${\mathrm{H}}^{\ensuremath{-}}$ ions and anion vacancies present, and also by the intensity of the \ensuremath{\sim}5.0-eV exciting light. Theoretical calculations predict that for a $^{1}A_{1g}$ relaxation of the surrounding ions the $^{1}T_{1u}$ and $^{3}T_{1u}$ electronic states of the $F$ center are almost degenerate and \ensuremath{\sim}0.05 eV above the $^{3}A_{1g}$ state. The $^{1}T_{1u}\ensuremath{\rightarrow}^{1}A_{1g}$ and the $^{3}T_{1u}\ensuremath{\rightarrow}^{1}A_{1g}$ transition energies are predicted to be 2.2 and 2.9 eV, respectively.

Spatial Productivity Variations in Manufacturing: A Critical Survey of Cross-Sectional Analyses

Abstract: This paper examines recent work on productivity variations over space. Labor productivity and labor productivity controlled for capital intensity both vary among regions and across city size. Urban...

Characteristics and Use of Burrows by Four Species of Armadillos in Brazil

Abstract: An investigation of four species of armadillos ( Priodontes maximus, Euphractus sexcinctus, Cabassous unicinctus , and Cabassous tatouay ) revealed differences in their burrow dimensions and choice of burrow sites. Measurements of burrow width alone separated P. maximus and C. unicinctus from E. sexcinctus and C. tatouay ; those of burrow height separated all three genera, but not C. unicinctus from C. tatouay . Together, these two measurements were adequate to identify the burrows of each species. The slopes of the burrow and of the surface around the burrow, and the direction at which the burrow entrance was dug, were similar for all four species. The time spent in a burrow and the type of site into which burrows were dug differed among species.

Renewable Energy Sources and Developing Countries

Abstract: The role of renewable energy sources in meeting the energy needs of developing countries is examined in the context of the burgeoning fuel prices and the associated geopolitical realities and economic burdens. The acute energy needs and the unavailability of commercial fuels in the rural areas offer a rewarding opportunity for the utilization of locally available renewable energy sources. Small-scale decentralized integrated system concepts for harnessing renewable energy sources are discussed. The basic economic factors involved in the introduction of renewable energy sources in the rural areas of developing countries are outlined to assist the designer in the selection of appropriate components and system concepts.

Caffeine hazards and their prevention in germinating seeds of coffee (Coffea arabica L.).

Abstract: The inhibition of growth of seedlings of coffee (Coffea arabica L.) exposed to 10 m M caffeine was found to occur in the rootlet: mitosis and cell plate formation were also inhibited. Since concentrations of endogenous caffeine in the imbibed seed are 40-60 mM, 4-6 times as high as in the seedlings, we conclude that coffee embryos have specific means of avoiding caffeine autotoxicity. Observations indicate that cell divisions in root tips start only after the latter are pushed away from the caffeine-rich endosperm by elongation of the hypocotyl and maintained through cell elongation. Caffeine is introduced into the embryonic cotyledons mostly after cell division is completed there. Thus, coffee seedlings may avoid autotoxic effects of endogenous caffeine by separation between sites where mitosis is occurring and those where caffeine is stored. This is achieved in root tips by separation is space but in the cotyledons by separation in time. Caffeine is liberated from the tree litter in coffee plantations and eventually will produce autotoxic effects, resulting in some degeneration.

The Time Crunch Wife's Employment and Family Work

Abstract: The relationship between patterns of time spent in household work and employment hours of the wife was examined in a sample of 206 families. Employment of the wife outside the home in paid work was significantly related to her time in housework, but had little effect on her husband's or children's time contributions to household tasks. A lessening of the time crunch for full-time employed wives and equalization of length of work days for husbands and wives was indicated when present data were compared with time budgets collected in the 1960s.

Loneliness and Interpersonal Judgments

Abstract: This study examines ratings of self and partners by high and low tested lonely college students following brief interactions with opposite sex strangers. Results replicate and extend previous findings, indicating more negative evaluations for high as compared to low lonely subjects in self ratings, ratings expected from partners; and for men only, ratings of partners. High lonely men were rated more negatively than low lonely men but the corresponding effect for women was not observed. The data also indicate that high lonely participants were perceived by their partners as more likely to rate themselves negatively. The findings are discussed in relation to the probable consequences of perceived social skill inadequacies for the experience of loneliness.

Determinism Revisited: Assault and Heat Stress in Dallas, 1980

Abstract: In the last few decades, social scientists have been reluctant to deal with the relationship between weather and human behavior, owing in part to the discredit brought to such studies by the excesses of the determinists. The few studies undertaken have generally relied on ambient temperature as a measure of stress. In the present work, a discomfort index was related to the incidence of aggravated assault in Dallas, Texas, for an eight-month period from March through October 1980. Some 4000 assault events were aggregated on a daily basis and related to three variables: discomfort index, day of the week, and month. The resulting model accounted for 71% of the variation in assault incidence. The discomfort index yielded significant F statistics whether entered first, second, or third in the model, indicating a significant main effect in spite of its collinearity with month. The analysis supports experimental laboratory evidence suggesting that heat stress is associated with aggressive behavior.

Seeds as allelopathic agents.

Abstract: Inhibitors of germination or of growth, highly diversified chemicals are commonly found in higher plants. They occur in vegetative organs as well as in seeds or other dispersal units. Nonprotein amino acids, when present, are mainly found in seeds where they can occur in extremely high concentrations. Density of seeds, rate of emanation of inhibitors, their amount and effectiveness, all determine allelopathic potential of seeds. To induce allelopathy, rate of emanation of inhibitors must be fast and of sufficient duration. Our observations in coffee seedsCoffea arabica L. indicate that rate of emanation of the inhibitor caffeine is highly enhanced during senescence of seeds, suggesting that when allelopathic potential of seeds is evaluated the presence of both young and old seeds should be considered. In many plants seeds are liberated close to the parent plant, the zone where seed-induced allelopathy may occur. Large numbers of seeds are usually produced in order to ensure establishment; greater number and mass of seeds may also increase allelopathic inhibition of competing vegetation.